This second Companion deals with the ancient theories of the psyche. The essays range over more than eight hundred years of psychological enquiry and provide critical analyses not only of the ancient discussions of the nature of the psyche and its states, but of such central topics as perception, subjectivity, the explanation of action, and what it is to be a person. In examining the wide variety of the different psychological theories offered by the ancient thinkers, from the increasingly complex materialism of the Presocratics and Hellenistics to the dualism of Plato and Plotinus, the collection demonstrates that psychology had become a wide-ranging and sophisticated discipline long before Descartes. The essays will be of interest not only to ancient philosophers but also to all those studying psychology and its history